The exhaust gas from energy system consists of non-condensable gas and steam with sensible and latent heat, respectively. When a lot of latent heat is included in the exhaust gas, its recovery is very important to improve the system efficiency. For condensation from steam-gas mixture, analogy correlation of heat and mass transfer has been used as an approximation. The analogy method is eagerly expected for the design of heat exchangers where the heat transfer correlation has been empirically established. However, at the high concentration of steam, some modification is necessary on the mass transfer correlation because it is originated and estimated from the heat transfer correlation without condensation. Condensation heat transfer on a row of horizontal stainless steel tubes was investigated experimentally and new analogy relation taking account of the mass absorption effect on the wall was proposed. Based on this basic study, a thermal hydraulic prediction method for latent heat recovery exchangers was proposed. Furthermore two kinds of compact heat exchanger with staggered banks of small bare tubes were designed with the prediction method. The more compactness was obtained with the smaller tubes at a designed heat recovery. The thermal hydraulic behavior in the compact heat exchangers was experimentally studied with air-steam mixture gas. The experimental results agreed well with the prediction proposed in this study and the more compactness with the smaller tubes was proved. Finally the prediction method was used in the commercial design of home hot water supply system using natural gas and the thermal efficiency was raised by 17 % with the latent heat recovery technology.
The present article contains a review of the literatures on the creep buckling of shell structures published from late 1950's to recent years. In this article, the creep buckling studies on circular cylindrical shells, spherical shells, partial cylindrical shells and other shells are reviewed in addition to creep buckling criteria. Creep buckling is categorized into two types. One is the creep buckling due to quasi-static instability, in which the critical time for creep buckling is determined by tracing a creep deformation versus time curve. The other is the creep buckling due to kinetic instability, in which the critical time can be determined by examining the shape of total potential energy in the vicinity of a quasi-static equilibrium state. Bifurcation buckling and snap-through buckling during creep deformation belong to this type of creep buckling. A few detailed descriptions are given to the bifurcation and snap-through type of creep buckling based on the present authors' works.
This paper is a review of the most influential approaches to developing beam models that have been proposed over the last few decades. Essentially, primary attention has been paid to isotropic structures, while a few extensions to composites have been given for the sake of completeness. Classical models - Da Vinci, Euler-Bernoulli and Timoshenko - are described first. All those approaches that are aimed at the improvement of classical theories are then presented by considering the following main techniques: shear correction factors, warping functions, Saint-Venant based solutions and decomposition methods, variational asymptotic methods, the Generalized Beam Theory and the Carrera Unified Formulation (CUF). Special attention has been paid to the latter by carrying out a detailed review of the applications of 1D CUF and by giving numerical examples of static, dynamic and aeroelastic problems. Deep and thin-walled structures have been considered for aerospace, mechanical and civil engineering applications. Furthermore, a brief overview of two recently introduced methods, namely the mixed axiomatic/asymptotic approach and the component-wise approach, has been provided together with numerical assessments. The review presented in this paper shows that the development of advanced beam models is still extremely appealing, due to the computational efficiency of beams compared to 2D and 3D structural models. Although most of the techniques that have recently been developed are focused on a given number of applications, 1D CUF offers the breakthrough advantage of being able to deal with a vast variety of structural problems with no need for ad hoc formulations, including problems that can notoriously be dealt with exclusively by means of 2D or 3D models, such as complete aircraft wings, civil engineering constructions, as well as multiscale and wave propagation analyses. Moreover, 1D CUF leads to a complete 3D geometrical and material modeling with no need of artificial reference axes/surfaces, reduced constitutive equations or homogenization techniques.
The constitutive equations for rubbers that are derived based on the molecular chain network model and their generalization to account for the non-affine deformation and viscoelastic deformation of rubbers are presented for the evaluation of the complex deformation behaviors under monotonic and cyclic deformation at different strain rates. Several applications of the constitutive equations using the finite element homogenization method for the evaluation of microscopic to macroscopic deformation behaviors of particles such as carbon black and silica-filled rubbers are addressed. The typical deformation behavior of rubbers and the essential mechanism of enhancement in the mechanical characteristics of particle-filled rubbers under monotonic and cyclic straining are clarified focusing on findings from our recent works.
Direct numerical simulations (DNS) of multi-fluid and multiphase flows have progressed enormously over the last decade or two. It is, in particular, now possible to simulate the evolution of hundreds of bubbles in laminar and turbulent flows for a long enough time so that meaningful statistical quantities can be collected. For bubbly flow in vertical channels DNS have provided considerable new insight into the structure of the flow and how it can be modeled. The flow structure depends sensitively on the sign of the lift force on the bubbles. For nearly spherical bubbles in both upflow and downflow the lateral migration of bubbles results in a core region where the weight of the mixture exactly balances the imposed pressure gradient. For upflow bubbles accumulate at the wall but for downflow the region next to the wall is free of bubbles. The results lead to a very simple model of the void fraction distribution and, for downflow the velocity and the flow rate can be predicted relatively accurately. Deformable bubbles result in a very different flow structure, with no bubbles accumulating at the wall. Simulations of the transient motion show that it takes a long time for the flow to reach a steady state and that the evolution is complex, with bubbles moving in and out of the wall-layer. The availability of DNS results calls for more intense efforts to use the data for developing closure terms for models of the average and large-scale flows, as well as the development of efficient and accurate methods for more complex flows, such as those undergoing topology changes and involving additional physical effects like surfactants and heat and mass transfer.
The present article is intended to give a broad overview and present details on the Lie symmetry induced statistical turbulence theory put forward by the authors and various other collaborators over the last twenty years. For this is crucial to understand that our present text-book knowledge proclaims that Lie symmetries such as Galilean transformation lie at the heart of fluid dynamics. These important properties also carry over to the statistical description of turbulence, i.e. to the Reynolds stress transport equations and its generalization, the multi-point correlation equations (MPCE). Interesting enough, the MPCE admit a much larger set of symmetries, in fact infinite dimensional, subsequently named statistical symmetries. Apart from the MPCE also the two other known complete theories of turbulence, the Lundgren-Monin-Novikov (LMN) hierarchy of probability density functions and the Hopf functional theory, share this property of admitting both classical mechanical and statistical Lie symmetries. As the Galilean transformation illuminates fundamental properties of classical mechanics, the new statistical symmetries mirror key properties of turbulence such as intermittency and non-gaussianity. After an introduction to Lie symmetries have been given, these facts will be detailed for all three turbulence approaches i.e. MPCE, LMN and Hopf approach. From a practical point of view, these new symmetries have important consequences for our understanding of turbulent scaling laws. The symmetries form the essential foundation to construct exact solutions. Presently we detail this only for the infinite set of MPCE, which in turn are identified as classical and new turbulent scaling laws. Examples on various classical and new shear flow scaling laws including higher order moments will be presented. Even new scaling have been forecasted from these symmetries and in turn validated by DNS.